1. Field of the Invention
The present invention relates to methods and apparatus of handling tubulars in and around a wellbore. More particularly, the invention relates to methods and apparatus to facilitate the formation of tubular strings. More particularly still, the invention relates to apparatus and methods for remote controlling the tubular connection process. More particularly still, the invention relates to methods and apparatus for supporting a string of tubular riser for use between an offshore oil and gas platform and the ocean floor.
2. Description of the Related Art
Wells are drilled and produced using strings of tubular that are threaded together. For example, wellbore are formed by disposing a drill bit at the end of a drill string. Due to the torsional forces present when rotating a bit at the end of the string that may be thousands of feet long, the connection in drill string include a shoulder that can be torqued to a certain value. Other tubulars that line a borehole or serve as a fluid path for production fluids have a simpler threaded connection that only has to be fluid tight.
With the advent of offshore drilling, a riser is commonly used to isolate drill string or production tubing from the ocean water. Riser is relatively large diameter tubing that extends between an offshore rig floor and a wellhead at the ocean floor. Because the well is sometimes in hundreds of feet of water, riser can be hundreds of feet long and must bend and sway with the ocean current and in some cases, with the movement and drift of a platform at the surface. In addition to its relatively large diameter, riser typically has a large upset portion at one end where it is threadedly connected to another piece of riser to form a string.
Due to its function of providing isolation between possible hazardous material and the ocean, it is desirable not to damage, scratch, or mar the outer surface of riser with tongs or other gripping devices that are typically used to date on a rig floor to connect sequential pieces of tubular pipe. For example, tubular strings are made today at a well site with the use of an elevator that can grasp a piece of tubular, lift it above the well center, and lower it into a threaded portion of another tubular extending from the well. Once the tubulars are connected, the elevator then lowers the entire string to a position where it can be grasped by another gripping apparatus known as a spider.
At any time, either the spider or the elevator or both must be able to retain the string. The prior art elevators and spiders necessarily grasp the outer diameter of the tubulars in order to retain them axially. The spiders and elevators often use a die to enhance their ability to grip the tubulars. However, the die tends to damage, scratch, or mar the outer surface of the tubular body. While the collateral damage to the outside of the tubulars is of little concern with liner or casing, it is often unacceptable with riser.
There is a need therefore, for a method and apparatus for handing tubulars at a well that does not result in damage to the outer surface of the tubulars. There is also a need for remotely controlling the tubular handling or connection process. There is a further need for a method and apparatus that permits the formation of tubular strings without utilizing the outer surface of the tubulars for axial retention.